How coral loses its color and starves

You can click on this picture to enlarge it.
It shows what coral reefs look like in Florida.

Corals are marine animals from the class Anthozoa and exist as small sea anemone-like polyps, typically in colonies of many identical individuals. The group includes the important reef builders that are found in tropical oceans, which secrete calcium carbonate to form a hard skeleton. Those big structures of ocean skeletons are called coral reefs, and a lot of ocean life depends on them.

Here is where most corals are:

Corals host tiny algae called zooxanthellae that give them their color and a food source. But when they are stressed by too much heat or cold, many corals expel their algae and "bleach."

Corals are very sensitive to temperature changes and thrive within a narrow band of heat and cold: a temperature increase of just 1.8 degree Fahrenheit can trigger them to bleach. After severe bleaching, they often die.

Even thousand-year-old coral reefs can die this way.

It would be a huge loss for these "rain forests of the ocean" to die. Also, many colorful reef fish, turtles, sharks, lobsters, shrimp, sea urchins, sea stars, anemones and sponges depend on those coral reefs. When coral reefs are threatened, often whole marine ecosystems are in danger as well.

In addition, the economic losses would be enormous in regions that depend on reefs for food and tourism income. Coral reefs provide an estimated $375 billion in economic benefits each year globally.

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